Semiconductor devices are usually fabricated on single crystal substrates, in which the number of crystalline defects is kept to a minimum. It is known that crystal defects can function as charge trapping sites, charge generation sites, and sites for contamination, which are capable of degrading the performance of a semiconductor device. Recent trends in the semiconductor industry have been towards higher degrees of integration. A known method of increasing the packing density of integrated circuits is to form semiconductor devices in thin films of a semiconductor material overlying each other, which is a method known as silicon-on-insulator (SOI). The method is known as SOI because thin films of silicon are deposited on an insulator, such as an oxide. In principle, multiple layers of such structures are possible, provided that the number of crystalline defects can be kept sufficiently low. Unfortunately, it is difficult to form monocrystalline layers over insulating materials such as an oxide, since these materials typically do not have a lattice structure. If a thin film of silicon is deposited over an oxide, for example, then the resulting film will have an amorphous or a polycrystalline structure. Such structures have a high density of Tam states (localized electronic states due to disorder). The disorder occurs because of crystalline defects such as grain boundaries, dislocations and intersticials. In order to achieve a monocrystalline layer of a material over an oxide, it is necessary to provide an oriented seed layer on the oxide, which can then be used as a lattice suitable for homoepitaxial or heteroepitaxial growth.
A known method for the manufacture of ribbons of polysilicon is taught by Israel A. Lesk in U.S. Pat. No. 4,027,053 entitled "Method of Producing Polycrystalline Silicon Ribbon" and assigned to the assignee hereof. The method uses a seed of silicon particulates which are broadcast on a quartz belt. The particulate sizes are generally in the range of 0.5 to 2 mils in diameter. A chemical vapor deposition process is used to grow a layer of polycrystalline silicon over and above the silicon particulates. The process forms a ribbon of polycrystalline material which is useful in the manufacture of solar cells. The ribbon can be converted into monocrystalline material, for example, by contacting it with a monocrystalline semiconductor material seed and heating the interface.